In comparing a conventional sealed alkaline storage battery using a sintered positive nickel electrode and a conventional sealed alkaline storage battery using a positive paste nickel electrode, the paste electrode is preferred since it is considered capable of providing a higher capacity.
A sealed alkaline storage battery using a paste nickel electrode is generally manufactured as follows. A nickel hydroxide powder is mixed with Co (cobalt), CoO (cobalt oxide), Ni (nickel) and/or other powder(s). These components serve as the electroconductive material which increase electroconductivity and minimize polarization. The resultant mixture is combined with an aqueous solution of a thickener, such as carboxymethylcellulose (CMC), and is kneaded to form a paste. The paste is then applied to a porous metal base plate or substrate, such as a foam nickel substrate, a fibrous nickel felt substrate or the like, in a manner so that the paste fills in the pores of the substrate. The pasted substrate is then dried and roll-pressed to produce a paste nickel electrode. This nickel electrode substrate is then used as a positive electrode for a battery. The positive electrode is paired with a negative electrode with a separator interposed between the positive and negative electrodes to make a battery element. The battery element is inserted into a battery container. Thereafter, an electrolyte is poured into the container and the container sealed to make a sealed alkaline storage battery which is useful in various fields. However, it has been observed that in the course of this storage battery manufacturing process, Co or CoO contained in the positive electrode dissolves in the alkaline electrolyte and, thereafter, deposits on the separator which can cause a short-circuiting of the battery.
Precisely how this short-circuiting of the battery occurs has not yet been fully determined, however, it is believed to occur when Co powder is oxidized by the oxygen in the atmosphere to form CoO which when brought into contact with the alkaline electrolyte forms HCoO.sub.2.sup.- ions. The chemical reactions of Co in the presence of oxygen and alkaline electrolyte is as follows: Co.fwdarw.CoO.fwdarw.HCoO.sub.2.sup.- .fwdarw.Co.sub.3 O.sub.4. The Co.sub.3 O.sub.4 is deposited on and in the separator as brown specks which cause the short-circuiting of the battery. Even when sealed off from air, the chemical reaction of CoO.fwdarw.HCoO.sub.2.sup.- nonetheless continues. In this event, although the diffusion of the ions in the electrolyte is relatively slow, they eventually pass through the separator to reach the negative electrode and, thereafter, during the charging operation, they then become reduced to Co to cause short-circuiting of the battery. Similar reactions also take place in the case of added CoO powder.
Accordingly, regardless of the presence or absence of oxygen, the dissolution of CoO in the alkaline electrolyte to HCoO.sub.2.sup.- goes on continuously. If oxygen from the atmosphere is present, Co.sub.3 O.sub.4 is deposited on the separator causing the short-circuiting of the battery. Additionally, HCoO.sub.2.sup.- ions pass through the separator to reach the negative electrode and, at the time of the charging operation, are reduced and cause short-circuiting of the battery.